Process and alloy for making ductile iron

ABSTRACT

A PROCESS FOR PRODUCING DUCTILE IRON COMPRISING ADDING TO A BATH OF LOW-SULFUR CAST IRON, A MATERIAL CONTAINING AT LEAST TWO GRAPHITE-NODULARIZING ELEMENTS. THE ADDITIVE MATERIAL CONTAINS EACH NODULARIZING ELEMENT IN RELATIVELY LOW CONCENTRATIONS SO THAT AFTER DISSOLUTION IN THE BATH THE CONCENTRATION OF NODULARIZING ELEMENTS REMAINING IS SUFFICIENT TO PRODUCE THE DESIRED STRUCTURE, BUT THE CONCENTRATION OF ANY ONE ELEMENT IS, OF ITSELF, INSUFFICIENT TO PRODUCE NODULAR (SPHEROIDAL) GRAPHITE.

March 26, 1974 A, B, MAL|Z|O ETAL 3,799,767

PROCESS AND ALLOY FOR MAKING DUOTILE IRON 5 Sheets-sheet 1 Filed OCT.. l5, 1971 MELTING DESULFURIZING V2 CASTING A. B. MALlzlo ErAL 3,799,767

PROCESS AND ALLOY FOR MAKING DUCTILE IRON -5 Sheets-Sheet 2 F/G. 3.

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Unted States Patent O 3,799,767 PROCESS AND ALLOY FOR MAKING DUCTILE IRON Andrew B. Malizio, Delran, and Martin A. Rice, Florence,

NJ., and Harry F. Brooks, Levittown, Pa., as signors to United States Pipe and Foundry Company, Birmingham, Ala.

Filed Oct. 15, 1971, Ser. No. 189,670 Int. Cl. C22c 37/02 U.S. Cl. 75-130 A 8 Claims ABSTRACT OF THE DISCLOSURE A process for producing ductile iron comprising adding to a bath of low-sulfur cast iron, a material containing at least two graphite-nodularizng elements. The additive material contains each nodularizng element in relatively low concentrations so that after dissolution in the bath the concentration of nodularizng elements remaining is sucient to produce the desired structure, -bu-t the concentration of any one element is, of itself, insufiicient to produce nodular (spheroidal) graphite.

BACKGROUND OF THE INVENTION The invention is in the field of metallurgy, more specifically, cast iron metallurgy, wherein the end products are ductile iron castings produced by either the permanent mold or sand casting procesees.

For many years the major commercial method for the production of ductile iron has been by the addition of magnesium in the form of magnesium containing alloys or by the addition of the pure element whereby the magnesium causes the graphite to solidify in the form of spheroids. The formation of graphite in this shape is responsible for the outstanding strength and ductility of the material.

There are many well-recognized disadvantages to the use of magnesium or magnesium-containing alloys, chief among them is that the reaction caused by addition of magnesium to molten iron is generally quite violent and accompanied by the formation of thick clouds of White smoke containing magnesium oxide particles. The reaction is also accompanied by brilliant white are that is harmful to vision. There are further disadvantages in that the high degree or reactivity makes it diliicult to obtain a high recovery of the added magnesium, hence the process is ineflicient. In addition to the poorer recoveries generally obtainable, the magnesium content of the melt decreases with time due to loss of magnesium from the bath by vaporization, by oxidation and by combination with any sulfur in the bath. The loss of magnesium is generally referred to in the art as fading Certain of the aforementioned disadvantages can be partially overcome depending on the manner of adding the magnesium or magnesium-alloy to the molten metal bath. For example, flash and are can be shielded from the eye by a protective cover. Also, somewhat greater eiciencies can be realized when the magnesium is added to the bath under pressure as opposed to pouring the molten metal on top of the magnesium-alloy. 'Ihese methods are generally undesirable from an economic and process viewpoint in that they require additional equipment to either enclose the arca where the magnesium additions are being made or to pressurize the vessel in which the additions are made. Such methods, particularly the pressurizing method, also add additional time and expense to the process.

On theother hand, it is known to the art that cerium is also a nodularizng element and is less reactive upon addition to molten cast iron thus overcoming the flare and smoke problem and also giving increased recoveries.

Despite the higher recoveries and lack of reactivity, cerium will still exhibit an undesirably high rate of fade. In addition, cerium is generally only eiiective in hypereutectic cast irons, it is a strong carbide former and, in our experience, has produced graphite particles that are not as perfectly shaped as those produced by the magnesium proess.

SUMMARY lOF THE INVENTION The nature of our work has been to develop a process for producing ductile cast iron that would solve some of the problems tolerated by the prior art. One of the objects of our invention is to reduce the amount of nodularizer required to produce nodular graphite in castings.

Another object of our invention is to reduce the fume and flare accompanying the addition of the nodularizng material.

A further object of our invention is to decrease the rate of fade of the nodularizng effect in the treated bath.

Yet another object of our invention is to provide `a process for minimizing the dross content of ductile iron.

Also an object of our invention is to provide a process allowing a selection of a number of individual nodularizers and quantities of individual nodularizers.

These objects are achieved in our preferred embodiment by adding to a bath of low sulfur cast iron two or more nodularizers in a silicon-iron alloy or mixture of siliconiron alloys wherein the alloy or mixture of silicon-alloys contains not more than three percent of any one nodularizer and the combination of all nodularizers in the alloy or mixture of alloys is not more than six percent with the resultant advantage being:

(a) a drastic reduction in fume and ilare when the alloy is added to the bath.

(b) a greatly decreased rate of fade of the nodularizing elfect.

(c) a reduction in total nodularizer required for a given casting.

(d) a reduction in the dross content in the castings.

DESCRIPTION OF DRAWINGS FIG. 1 is a schematic representation of the basic steps in the usual process of making ductile iron castings, and is not part of our invention.

FIG. 2 is a graphical representation showing the amount of effective nodularizng elements remaining in a bath of molten iron vs. holding time and comparing additions of one nodularizng element (as known in the prior art) t0 additions of more than one nodularizng element in accordace with our invention.

FIG. 3 is a photomicrograph of the graphite structure of a pipe cast after prolonged holding of a melt to which 5 nodularizng elements were added pursuant to our invention.

PIG. 4 is a graphical representation comparing the percentages of the original additions remaining in a bath of cast iron vs. holding time and comparing additions of one nodularizng element (as known in the prior art) to additions of more than one nodularizng element in accordance with our ivention.

FIG. 5 is a graphical representation of the amount of 2 nodularizng elements remaining in pipe made under production condition vs. time after addition according to our invention.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is schematically represented the usual process for producing ductile iron castings. Our invention relates to the nodularizng step, those preceding steps being well known to one skilled in the art. The relationship between nodularizing agents used, the manner of use and the nodularizing effect forms the basis of our invention.

Our invention lies in the discovery that the total amount of nodularizing agents needed to produce ductile iron can be reduced if more than one nodularizing element is added in proper amounts. This allows a reduction in the concentration of the nodularizing elements in the bath which in turn improves eiiiciency, gives longer eiective life, i.e., reduce fading, minimizes flare and smoke and minimizes the tendency for the iron to form dross.

The following results shown in Tables I and II were obtained from nodularizing individual heats of molten low sulfur cast iron as indicated:

TABLE I Total amount Total remaining in melt after- Elements added, Test added percent 1 min. 5 mln. 10 min. 15 min. 20 A Mg 0. 05 .022 .016 .011 .008 B Ce o. 05 037 .019 .011 003 c 030i (iii 0i?? oi g 1 +C@ i l 0- 05 021) 020) 015) 014) 034 020 025 022 D Mg 00s) (.007) (.000) (.005) 25 +C@ 008) 000) 005) 004) +Le 2 0. 05 0085) 005) 0025) 001) +Nd 005) 005) 0005) 010) +Y 005) 005) 005) 002) 1 0.025 Mg+0.025 Ce. 2 .01% of each of 5 elements. 3()

Norm-Numbers in parentheses represent amount of individual elements.

for each Test A through D is plotted as a function of time, versus the amount of nodularizer originally added to the bath. It can be seen, from FIG. 2, that magnesium and cerium contents fade in time to lower and lower levels and at some point in time, the content is insucient to produce a good spheroidal graphite structure. In the centrifugal casting of pipe in metal molds, we have found that in cast irons having sulfur contents of the order of 0.004 percent to 0.006 percent, the minimum range of magnesium content needed to insure a graphite structure in 6 inch diameter pipe in which approximately 90 percent of the graphite consists of well-formed spheroids, is 0.012 to 0.014 percent magnesium. In the case of cerium the required residual content has been found to be approximately 0.016 percent. Thus, after 10 minutes holding time, neither magnesium nor cerium, when added alone as shown in curves A and B of FIG. 2, is present in suflicient quantities, in the melt, to insure the desired graphite structure, i.e. both quantities are below the critical level.

In contrast to the behavior of magnesium or cerium when added individually in amounts of .05 percent, the addition of smaller amounts (.025 percent) of magnesium and cerium together or .0l percent of each of five nodularizing elements, results in more effective utilization of the nodularizing addition both from the standpoint of higher initial recoveries and longer effective life. Thus, it can be seen from curves C & D the total nodula-rizing content of the baths are over 0.02 percent even at fifteen minutes after addition.

We have further discovered that the various nodularizing elements diier in their nodularizing power when In each Test A through D as listde in the above tables, the molten bath of low sulfur cast iron, prior to the nodularizing step, was comprised of the following ele- In Test A the mangnesium addition of 0.05 percent by weight of iron was in the form of a commercial, ceriumfree, magnesium ferrosilicon having a magnesium content of 6.17 percent. In Test B 0.05 percent by weight of pure cerium metal chips was added to the bath. In Test C the magnesium and cerium additions were made in the form of an alloy containing 3.0 percent magnesium plus 3.0 percent cerium, 45 percent silicon, balance iron. The total nodularizing addition of .05 percent by weight consisted of 0.025 percent magnesium plus 0.025 percent cerium. In Test D, again the total nodularizing addition amounted to 0.05 percent by weight. In this instance the nodularizing addition consisted of 0.01 percent each of the following ve elements: magnesium, cerium, lanthanum, neodymium and yttrium. Magnesium and cerium were added in the form of a ferrosilicon alloy containing 3% magnesium and 3% cerium. Lanthanum and neodymium were added in the metallic form; the neodymium contained 74 percent neodymium and 14 percent praseodymium. The yttrium was added in the form of a ferro silicon containing percent yttrium.

The results listed in Tables I and II are likewise shown graphically in FIGS. 1 and 2 where the amount of nodularizer remaining in a bath of molten cast iron individually added to melts of cast iron; however, it appears that when added in combination, the combined total of the percentages of the nodularizing elements remaining in the melt can be used as an estimate of their nodularizing power in the melt.

As an illustration of this point, Table I shows the residual concentration of five nodularizing elements in a melt of cast iron at times up to 15 minutes after the addition of .01% of each element was made. A 6 inch diameter pipe was cast from this melt (Test D) at 18 minutes after the ve elements were added. This pipe had an acceptable nodular graphite structure as shown in FIG. 3. Since the residual amounts of the individual nodularizing elements in this melt are so minute, as shown in Table I, the structure in FIG. 3 could only have resulted from the combined nodularizing power of all the elements present. It is also indicated in Table I that the sum total of nodularizing elements remaining in the heat -required to produce an acceptable graphite structure in pipe is of the same order of magnitude as (the residual amount of) magnesium alone or cerium alone (which would be required to produce the same acceptable graphite structure, as earlier stated).

The cu-rves shown in FIG. 2 were established by adding only one of the nodularizing elements or combinations of the elements to baths of molten cast iron containing the following range of indicated elements in the nal composition.

Percent Total carbon 3.4-3.6 Silicon 2.7-2.9 Manganese 0.25-0.30 Sulfur 0.004-0.008 Phosphorus 0.04-006l Percent Total carbon 3.4-3.6 Silicon 1.9-2. 1 Manganese (12S-0.30 Sulfur 0.005-0.012 Phosphorus 0.04-0.06

Data from these Production tests are tabulated in Table III.

cent. In this test 8" diameter pipe, cast 31 minutes after a nodularizing treatment, contained 0.011 percent magnesium plus 0,012 percent cerium for a total of .023 percent (magnesiumH-cerium). The total weight of nodularizing elements in the molten bath of cast iron being from about 0.03 to 0.12 percent of the weight of the bath. This represents a recovery 56 percent of the original amount, and verifies that the high recoveries and longer etective life of the nodularizing elements can be obtained by the simultaneous addition of separate alloys each containing a nodularizer, or by the addition of one alloy containing more than one nodularizer. \In these plant trials using the alloy containing 2.5 percent magnesium {-2.4 percent cerium, the liar-ing and evolution of smoke generally associated with adding magnesium-containing alloys were virtually eliminated.

TABLE Inf-DATA FROM PRODUCTION TESTS Percent Remaining Total Chai-py notched Impact Time from nodularizer in pipe remaining addition until pipe in pi e Ultimate Yield Percent Plus was cast, minutes Mg Ce Mg+ e strength strength elong. percent -40 F.

The additions consisted of magnesium ferrosilicon (containing 5 percent magnesium) plus an addition of cerium ferrosilicon (containing 10 percent cerium). The amounts added were .025 percent magnesium +0.25 percent cerium for a total nodularizing addition of .05 percent. The tests showed that pipe having good spheroidal graphite structures could be cast at times as long as 34 minutes after the additions were made. The data illustrated in Table III is shown graphically in FIG. 5. The curves in FIG. 5 show that pipe cast 34 minutes after addition of magnesium-i-cerium were found to contain .013 percent magnesium H-.OlO percent cerium. The salient feature of these data is that neither element is present in suicient quantity to insure the production of 4good spheroidal graphite structures by itself; however, the combined total content of nodularizing elements (.023 percent) is suflicient to produce the desired graphite structure. This is also illustrative of the eiiiciency and longer eiective life obtained by small additions of nodularizing elements since the residual content of magnesium-l-ceri-um (.023 percent) represents a recovery of 46 percent of the original total nodularizing addition 34 minutes after the addition was made. Also included in Table III are the results of mechanical tests which are indicative of the structures obtained in the pipe. These pipe met the stringent requirements of commercial specifications for notched impact resistance as well as tensile properties.

Another series of tests were conducted under production conditions to determine whether or not the results obtained by the combined addition of two separate alloys (magnesium ferrosilicon plus cerium ferrosilicon) could be obtained by the addition of one alloy containing both magnesium and cerium. In these tests six-ton batches of cast iron were treated with additions of an alloy containing 2.5 percent magnesium plus 2.4 percent cerium. In one test an addition of 0.83 percent of this alloy, |by weight, was made. This amounted to an addition of .021 percent magnesium plus .020 percent cerium, for a total nodularizing addition of 0.041 per- From the foregoing it is apparent that the addition of an alloy or mixture of alloys containing not more than 3% of each of two or more nodularizers in small quantities will assure that suicient nodularizers will be present over a longer period of time than when the same total quantity of one nodularizer is added and will eliminate any violent reaction accompanying the addition. This phenomenon is quite surprising and is not fully understood.

In experiments using this 2.5% magnesiumH-2.4% cerium alloy for making sand castings it was found that acceptable graphite structures could be produced with additions of nodularizing elements that lwere 20% less than required with a conventional 5% magnesium ferrosilicon. With this reduction less alloy addition is required and this in turn reduces the amount of dross formed.

Although the preferred embodiment of the present invention has been described, it will be understood that it is intended to cover all changes and modifications of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

We claim:

1. A process for making ductile iron castings characterized by reduced fuming and flaring and decreased rate of fade of .the nodularizing elfect in the treated bath, and in which free graphite exists mainly in the form of spheroids comprising the following steps:

(a) forming a molten bath of low sulfur cast iron,

(b) adding to the bath magnesium and at least one other nodularizing element, each in an amount up to about .03% by weight of the bath but less than that needed to produce ductile iron in which approximately at least of the graphite exists as well-formed spheroids, said magnesium being in an alloy in which the amount of said magnesium is no more than about 3% by weight while the total amount Aof vnodularizing agents added being at least about .03% to .12% by weight of the bath,

(c) pouring castings from said bath, and

(d) allowing said castings to solidify.

2. A process for making ductile iron castings comprising the following steps:

(a) forming a molten bath of low sulfur cast iron,

(fb) adding to the bath an alloy comprising at least two nodularizing elements selected from the group consisting of magnesium, cerium, yttrium, lanthanum, neodymium and praseodymium, the total weight of said at least two nodularizing elements being not greater than 6% of the weight of said alloy, and the weight of any one of said nodularizing elements being not greater than 3% of the weight of saidalloy and the weightof said nodularizing elements being from 0.03 to 0.12 percent of the Weight of said bath, and the amount of each of said at least two nodularizing elements alone being less than required to produce ductile iron in which approximately 90% of the' graphite exists as well-formed spheroids,

(c) pouring castings from said bath, and

(d) allowing said castings to solidify.

3. A process as in claim 2 wherein one of said at least two nodularizing elements is magnesium in an amount of up to 3 percent by IWeight and the remaining nodularizing elements of said at least two nodularizing elements include up to 3 percent iby weight of each of said remaining nodularizing elements.

4. A process as in claim 2 wherein said at least two nodularizing elements consist of magnesium and cerium, said magnesium and cerium each being present in amounts up to '3 percent by Weight of said alloy.

5. A process for making ductile iron castings comprising the following steps:

(a) forming a molten bath of low sulfur cast iron,

(b) adding to said bath a mixture of alloys, each alloy of said mixture comprising at least one nodularizing element selected from a group consisting of magnesium, cerium, yttrium, lanthanum, neodymium and praseodymium, the total weight of nodularizing elements in said mixture being from 0.03 to 0.12 percent of the weight of said bath, each nodularizing element being different from any other nodularizing 8 element in said mixture, and the amount of each nodularizing element alone being less than required to produce ductile iron in which approximately 90% of the graphite exists as well-formed spheroids, magnesium, if used, being present in the alloy in an amount of from 1 to 3% by weight of said alloy,

(c) pouring castings from said bath, and

(d) allowing said castings to solidify.

6. A process as in claim 5 wherein the nodularizing elements in said mixture of alloys comprise up to 6% by weight of said mixture of alloys.

7. A process as in claim 5 wherein said mixture consists of a iirst alloy and a second alloy, said first alloy comprising only one nodularizer, said second alloy comprising at least onenodularizer, said rst alloy comprising magnesium in an amount up to 3 percent by Iweight and said second alloy comprising up to 3 percent by weight of each of the remaining nodularizing elements.

8. A process as in claim 5 wherein said mixture of alloys consists of a rst alloy comprising only one nodularizer and a second alloy comprising only one nodularizer and said first alloy comprises up to 3 percent magnesium by weight of said rst alloy and said second alloy 'comprises up to 3 percent cerium by weight of said second alloy.

References Cited UNITED STATES PATENTS 1,555,978 10/1925 Hunt 75-130 A 2,542,655 2/ 1951 Gagnebin et al. 75-130 A X 2,555,014 5/1951 Strauss 75-130 A X 2,792,300 5/ 1957 Livingston 75--130 A 2,816,829 12/1957 Bogart 75-130 A 2,841,489 7/ 1958 Morrogh 75-130 A X 2,841,490 7/ 1958 Steven et al. 75-130 C 2,867,555 1/1959 Curry 75-130 A X 2,873,188 2/1'959 Bieniosek 75130 A 2,877,111 3/1959 Barnes et al. 75--130 C 3,155,498 11/1964 Jandras 75-130 C 3,459,541 8/1969 Hohl et al. 75-130 A CHARLES N. LOVELL, Primary Examiner P. D. ROSENBERG, Assistant Examiner U.S. Cl. X.R. -130 B, 130 C Patent No. -37-99767 Dated Marh 26, 1974 Andrew B. Malzo et al. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2,4lne 6, "proess" should read process line 6l, "vent'on" should read f-vinvention Column 3, line l0, "reduce" should read reduces lne 42, "lstde" v should read listed line 52, "mangnesum" should read fv. magnesium Column 5 line 3, "nodularzes'v',` should read nodularzers Column 6, lines 4-7, cancel "The ltotall weight of nodularzng elements in the molten bath of cast iron being from about 0.03 to 0. l2 percent of the weight of the bath. line elements added tojthemolten bath of cast iron being from vabout 0.03 to 0.12 percent of the weight of the bath.

Signed andv sealed this '24th day of Septemberl 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents l v USCOMM-DC 60376-P69 t u.s. GOVERNMENT HUNTING orncz: |90 o-su-asd,

ORM PO-l 050 (iO-69) 43, after "'addton. insert The total weight of. nodularzng 

